Closing device in an injection moulding machine for synthetic materials

ABSTRACT

The invention relates to a clamping device for an injection molding machine for plastics, including a fixed platen ( 11 ) and an end platen ( 19 ) which is connected to a moving platen ( 12 ) by means of toggle mechanism ( 13 ). A hollow-shaft motor ( 7 ) cooperates with a spindle ( 21 ) and is arranged between the end platen ( 19 ) and the moving platen for operating the toggle mechanism. According to the invention, one or more carrier arms ( 23, 24 ) are arranged laterally to and/or beneath the hollow-shaft motor ( 7 ) for movable support of the hollow-shaft motor.

[0001] The invention relates to a clamping device according to the preamble of claim 1.

[0002] EP 0658 136 B1 discloses a clamping unit for molding tools of injection molding machines, including a clamping system in the form of a toggle mechanism, disposed between the moving platen and an end platen, for displacing the moving platen. Several so-called five-point toggle lever systems are coupled with a common crosshead. A threaded spindle is connected in fixed rotative engagement upon the crosshead and engages a nut which is immobile in axial direction but received in the end platen for rotation. The rotary drive is implemented by coupling the nut to a hollow shaft of an electric motor which is flange-mounted to the outside of the end platen. The hollow shaft is internally so dimensioned as to be suitable to easily receive the entire length of the threaded spindle, when the threaded spindle extends rearwards out of the nut. The toggle lever systems are in symmetric relationship to the force axis of the clamping unit, and the threaded spindle, the spindle nut and the electric motor with its hollow shaft are in alignment with the force axis of the clamping unit. A similar system is described in DE-PS 195 24 314 C1.

[0003] These systems have shortcomings relating to a comparably long construction of the clamping device because the electric motor is arranged outside the end platen and the inner dimension of the hollow shaft is suited to the spindle length.

[0004] In accordance with U.S. Pat. No. 5,804,224, this drawback is eliminated by arranging the hollow-shaft motor either on the inner side of the end platen (U.S. Pat. No. 5,804,224, col. 3, lines 60 to 63) or to secure the hollow-shaft motor on the crosshead of the toggle mechanism (U.S. Pat. No. 5,804,224, FIG. 1).

[0005] When the hollow-shaft motor is secured to the crosshead, the weight thereof must be borne by the spindle, on one hand, and by the toggle mechanism, on the other hand. This has an adverse effect on the joints of the toggle mechanism. Moreover, the spindle may sag. This is especially true when high-power and accordingly heavy hollow-shaft motors are involved.

[0006] The invention is based on the object to provide a clamping device of this type, which does not subject the spindle as well as the joints of the toggle mechanism to significant stress, even when constructed of short configuration and used with heavy hollow-shaft motors.

[0007] This object is realized in accordance with the invention by the features of claim 1. As the hollow-shaft motor is movably supported on carrier arms, the spindle and the joints of the toggle mechanism are effectively freed from a weight load and there is no restriction as far as the selection of the hollow-shaft motors is concerned.

[0008] The subsequent claims set forth advantageous improvements of the invention.

[0009] According to an advantageous configuration of the invention, the end platen has a cylindrical recess in which the hollow-shaft motor can move into. As a consequence of this improvement of the invention, the structural length of the injection molding machine is reduced in any event by the thickness of the end platen. The recognition to configure the end platen with a cylindrical recess in which the hollow-shaft motor can move into, realizes a significant shortening of the structural space.

[0010] According to a preferred embodiment of the invention, the spindle is arranged in a rotationally fixed manner. The spindle end, facing the moving platen, is hereby in engagement with the rotor of the hollow-shaft motor, advantageously via a nut, and the stator of the hollow-shaft motor is connected to the toggle mechanism. As the motor runs, it moves axially and operates the toggle mechanism. In contrast thereto, the spindle is stationary and barely projects beyond the outer end of the end platen. This means that the structural length of the injection molding machine is essentially bounded by the end platen. The drawback of prior art injection molding machines with a clamping device driven by a spindle and a hollow-shaft motor which is flange-mounted to the outside of the end platen, to have a structural length which is greater than an injection molding machine with belt drive of the clamping device, is thus eliminated. The direct drive via a hollow-shaft motor and a spindle offers, however, many advantages in comparison with a transmission with toothed belt. This drive is safer in operation than a belt drive, which may fail, when the belt is ripped. The direct drive is service friendlier as a retensioning of the belt is eliminated. Compared to a belt drive, it is subjected to less dust because no dust can be encountered as a result of a belt drive. Moreover, it has a greater efficiency and does not cause rolling noises of the belt. The quality of control is significantly improved compared to a belt drive in which a belt acts as elastic element. As a consequence of the high stiffness of the spindle drive, no hysteresis exists. The drive system is faster because, despite higher mass inertia, the comparably smaller rotation speed enables to reach the target speed faster.

[0011] According to a variation of the invention, the spindle can be guided through the end platen and secured in a rotationally fixed manner in an anchor plate.

[0012] According to an alternative preferred embodiment of the invention, the spindle is connected in a rotationally fixed manner with the rotor of the hollow-shaft motor and meshes with a nut which is connected in a rotationally fixed manner with the end platen. The stator of the hollow-shaft motor is connected with the toggle mechanism. Compared to the first preferred embodiment of the invention, this has the drawback that the spindle is not rotationally fixed and stationary, but projects beyond the end platen, when the clamping device opens and the hollow-shaft motor moves in the direction of the end platen. Thus, the advantage of a smaller structural length is lessened again. The advantage in relation to the first preferred embodiment of the invention resides, however, in the fact that the hollow shaft can be directly connected with the spindle. As a consequence, the nut, connected to the hollow shaft and engaging the spindle, can be omitted. In view of its great mass and its great diameter, this nut has a significant moment of inertia, and thus constitutes a higher dynamic load in comparison to a rotatable spindle. The decrease of the dynamic load in the embodiment of the invention with rotatable spindle enables a quicker movement of the clamping device. The nut, connected in this embodiment in a rotationally fixed manner with the end platen, does not pose great demands as far as balancing is concerned. When especially high-quality injection molding machines are involved, in which the demand of space is secondary while very high dynamics should be realized, this alternative embodiment of the invention is especially advantageous.

[0013] The hollow-shaft motor is either flange-mounted directly onto the crosshead or integrated therein, for example, by providing the crosshead with a recess for receiving the hollow-shaft motor. As an alternative, the stator may also be coupled directly to the toggle mechanism via suitable connecting elements. As a consequence of the invention, the reaction moment of the drive and the guidance of the crosshead can be realized by a single cost-efficient construction.

[0014] According to an advantageous configuration of the invention, the end platen has a cylindrical prolongation for rotatable support of a sun wheel of an adjustment device of the end platen. The cylindrical prolongation affords the end platen with added stability. A sun wheel of steel and an end platen of spherulitic cast iron provide a good friction pair for a sliding bearing. Hereby only a minimal need for lubrication is required.

[0015] Exemplified embodiments of the invention are shown in the drawings, in which:

[0016]FIG. 1 shows a cross section of a clamping device according to the invention,

[0017]FIG. 2 shows a variation of the clamping device according to the invention of FIG. 1 with rotatable spindle.

[0018] An example of the invention is illustrated in the attached FIG. 1. Arranged on a machine bed 16 is a fixed platen 11, whereby a moveable platen 12 is able to move axially relative to the fixed platen by a toggle mechanism 13. The fixed platen 11 is connected via the machine bed 16 with an end platen 19. A spindle 21 is guided with its end distal to the moving platen through the end platen 19 and connected in a rotationally fixed manner in an anchor plate 3. Arranged on the other end of the spindle 21 is a hollow-shaft motor 7 and axially movable on carrier arms 23 which are arranged on both sides of the spindle 21 and fixed in the end platen 19 so that in FIG. 1 only the rear carrier arm 23 is partially visible. A spindle nut 5 is coupled with the hollow shaft or the rotor 6 of the hollow-shaft motor 7 and is in engagement with the spindle 21. The stator 4 of the hollow-shaft motor 7 is flange-mounted to the toggle mechanism 13. In this way, the functions of the crosshead and of the drive motor are united.

[0019]FIG. 2 shows an alternative embodiment of the invention in which the spindle 21 is connected in a rotationally fixed manner with the rotor 6 and meshes with a nut 22 which is connected in a rotationally fixed manner to the end platen 19. The stator 4 of the hollow-shaft motor 7 is connected to the toggle mechanism 13. The spindle 21 and thus the hollow-shaft motor 7 moves axially as the rotor rotates. The clamping device is opened and closed, respectively, via the toggle mechanism 13. When the clamping device opens, whereby the hollow-shaft motor 7 moves in the direction of the end platen 19, the spindle 21 projects beyond the end platen 19. As carrier arm is provided here a carrier arm 24 arranged beneath the hollow-shaft motor 7. This can be secured in the end platen 19 or—as shown here—can extend through the end platen 19 and be secured in the anchor plate 3. Optionally, lateral as well as lower carrier arms 23 and 24 may be provided.

[0020] Position List Injection Molding Machine 3 anchor plate 11 fixed platen 12 moving platen 13 toggle mechanism 16 machine bed 19 end platen 22 nut Drive 4 stator of the hollow-shaft motor 5 spindle nut 6 rotor of the hollow-shaft motor 7 hollow-shaft motor 21 spindle 23 lateral carrier arms 24 lower carrier arm 

1. Clamping device for an injection molding machine for plastics, comprising a fixed paten (11) and an end platen (19), which is connected via a toggle mechanism with a moving platen (12), wherein a hollow-shaft motor (7) interacts with a spindle (21) and is arranged between the end platen (19) and the moving platen for operating the toggle mechanism (13), characterized in that one or more carrier arms (23, 24) are provided laterally to and/or beneath the hollow-shaft motor (7) for movable support of the hollow-shaft motor.
 2. Clamping device according to claim 1, characterized in that the carrier arms (23, 24) are secured in the end platen (19).
 3. Clamping device according to claim 1 or 2, characterized in that the carrier arms (23, 24) extend through the end platen (19) and are secured in an anchor plate behind the end platen.
 4. Clamping device according to one of the claims 1 to 3, characterized in that the end platen (19) has a cylindrical recess in which the hollow-shaft motor (7) can move into.
 5. Clamping device according to one of the claims 1 to 4, characterized in that the spindle (21) is arranged in a rotationally fixed manner, that the end of the spindle (21), facing the moving platen (12), is in engagement with the rotor (6) of the hollow-shaft motor (7), and that the stator (4) of the hollow-shaft motor is connected with the toggle mechanism (13).
 6. Clamping device according to one of the claims 1 to 5, characterized in that the spindle (21) is guided through an end platen (19) and secured in a rotationally fixed manner in an anchor plate (3).
 7. Clamping device according to one of the claims 1 to 6, characterized in that the toggle mechanism (13) is coupled to a crosshead, and that the crosshead has a recess for receiving the hollow-shaft motor (7).
 8. Clamping device according to one of the claims 1 to 7, characterized in that the toggle mechanism (13) is coupled directly to the stator (4) of the hollow-shaft motor (7).
 9. Clamping device according to one of the claims 1 to 8, characterized in that the stator (4) of the hollow-shaft motor (7) is movably supported on the carrier arms (23, 24).
 10. Clamping device according to one of the claims 1 to 9, characterized in that the moving platen (12) is movably guided on several columns, and that these columns serve as carrier arms (23, 24) for the hollow-shaft motor (7) or the stator (4) of the hollow-shaft motor (7).
 11. Clamping device according to one of the preceding claims, characterized in that the end platen (19) has a cylindrical prolongation for rotatable support of a sun wheel of an adjustment device of the end platen (19). 